OBJECTIVE-C Study Notes _block

First, block syntax

Blocks: Block syntax, which is essentially an anonymous function (a function without a name), the implementation of the block variable holding function, which can be directly adjusted by the block variable. There is no post-extended version of Block,c language in standard C, plus anonymous functions. C + +, JS, swift and other language, there is a similar syntax, called closures. The block syntax is similar to a function pointer.

• Block type: Int (^) (int)
• Block variable: myblock
• Block value: ^ int (int num) {return 7 * NUM;}
• That is: ^ return value type (parameter list) {function Body} where the return value type can be omitted.

        / * block type: Int (^) (int, int) * block variable: BLOCK1 * Block's value: ^int (int x, int y) {return x + y;}; ^ return value type (parameter list) {function Body} (The return value type can be omitted) */        / * 1. No return value, no parameter of block * /        void(^BLOCK3) () = ^()        {NSLog(@"Hello, world!.");        }; Block3 ();/ * Block call * /        / * 2. No return value, parameter * /        void(^BLOCK4) (int,int) = ^(intXintY) {NSLog(@"%d", x + y);        }; Block4 (3, $);/ * 3. There is a return value, no parameter * /        int(^BLOCK5) () = ^()        {return  -; };NSLog(@"%d", Block5 ());/ * 4. There are return values, parameters * /        int(^BLOCK6) (int,int) = ^(intXintY) {returnx > y?        x:y; };NSLog(@"%d", Block6 (3,5));

Second, block to make?

int (^block1)(intint y) = ^(intint y) {  return x + y;};int a = block1(3234);  // block的使?和函数指针的使用类似NSLog(@“%d”, a);  // 打印结果：66

Block into the typedef.

• typedef int (^BLOCKTYPE) (int x, int y)

• Primitive type: Int (^) (int x, int y)

• New Type: Blocktype

/* Block typedef */typedefint(^blockType)(intint);blockType block1 = ^(intint y) {            return x + y;        };NSLog(@"%d", block1(35));

Block notation

int (^block1)(intint y) = ^(intint y) {  return x + y;};

BlockType block1 = ^(intint y) {  return x + y;};

The above two implementations are equivalent.

Blcok and local variables and global variables

        / * global variable defined outside the main function * /        intn = -;/* Knowledge point 4 block vs. local variable global variable */        / * Local variable * /        intA = -;int(^block) () = ^() {returnA };NSLog(@"%d", block ());int(^BLOCK2) () = ^() {//A = $;            returnA };/* Summary: By default, block can access but cannot change local variables */__blockintb = $;int(^BLOCK3) () = ^ () {b = -;returnb };NSLog(@"%d", Block3 ());/* Summary: Using __block modified local variables, block inside can change the value */        /* Block and global variables */        int(^BLOCK4) () = ^ () {n = $;returnN };NSLog(@"n =%d", Block4 ());Static intnum =1;int(^BLOCK5) () = ^ () {num =8;returnNum };NSLog(@"num =%d", Block5 ());

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OBJECTIVE-C Study Notes _block